The third plague of Egypt, Exodus 8:16; Psalm 105:31; peculiarly offensive to the priests, who were obliged to shave and wash their entire body every third day, lest they should carry any vermin into the temples. According to many interpreters, lest they were the small stinging gnats which abound in Egypt.
Although written in 1859 by William Rand, this dictionary of the Bible from the American Tract Society is still relevant today.Wikipedia
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